Concerted Proton-Coupled Electron Transfer by Mo⁵⁺/Mo⁶⁺ Reversible Transformation for CO₂ Photoreduction with Nearly 100% CH₄ Selectivity

Regulation of the proton-coupled electron transfer (PCET) process to avoid the unbalanced proton and electron regions on the reduction active sites is key to dictating product selectivity in a photocatalytic CO2 reduction reaction. Here, we show that reversible Mo5+/Mo6+ as a mediator can regulate the proton and electron transfer process at the Bi2MoO6 nanosheet/In2O3 microtube (BI) catalyst. The formed concerted proton-coupled electron transfer enables a champion solar-to-methane efficiency of 0.15%, resulting in nearly 100% CH4 selectivity and a competitive CH4 yield of 46.37 μmol g–1 h–1 in pure water. The experiments, together with theoretical calculations, clearly validate that In sites as H2O oxidation centers provide protons, and the regulation of protons and electrons by using Mo sites forms approximate electroneutral proton/electron pairs, which are conjointly transferred to Bi sites as CO2 adsorption/reduction centers, thus achieving precise hydrogenation on Bi sites for binding of the *CH3O key intermediate to form CH4.